In the 1980s, even before precisely understanding the mechanisms involved, health professionals began to practice bright light therapy (BLT) to treat a chronobiological disorder found mostly in northern countries—seasonal affective disorder, or SAD, a form of depression occurring during winter months. Researchers have concluded that SAD is caused by a chronic lack of sunlight beginning in the autumn, as well as habits of modern life that lead us to spend most of our days indoors under artificial lighting. The person’s internal clock no longer receives the necessary signals to properly synchronize the circadian rhythm, causing a cascade of secondary effects such as insomnia, lack of energy, and depression.
The proposed solution to SAD is simple: expose the person to a light source sufficiently bright to allow the system to resynchronize with the circadian rhythm. The prescription typically involves the use of a lamp providing 10,000 lux for thirty minutes a day, preferably upon waking. The therapy lamp must have a spectrum wide enough to include the wavelengths capable of stimulating the nonvisual optic pathway (centered on blue at 460–490 nm) because that is the best way to reach the master internal clock, the suprachiasmatic nucleus, or SCN. There currently are several types of these lamps.
Numerous studies have now established that bright light therapy is at least as effective for SAD as any medication that would be prescribed. Its success is such that it is commonly thought of as being synonymous with light therapy, even though light therapy encompasses a much wider field than the sole bright light therapy technique.
The lack of light in wintertime affects many more people than we might think: for example, it is estimated that 10 to 15 percent of the population of France suffers from mild seasonal depression, the “winter blues,” even if they do not present some of the more extreme symptoms of SAD. For those people as well, an occasional dose of bright light (using the same lamps as for SAD) can make all the difference in the world.
Today the use of bright light therapy is also being explored in the treatment of sleep disorders, eating disorders, and Parkinson’s disease. It has been observed that the technique can also be helpful for forms of depression other than SAD.
What About Jet Lag?
Jet lag is a perfect example of the desynchronization of one’s internal clock, and most of us occasionally have to deal with it after lengthy air travel. Bright light therapy can be used in an attempt to minimize its impact, but studies have shown that the results do not necessarily justify the effort. That’s because the resynchronization of one’s internal clock follows its own natural rhythm, which is difficult to speed up, even with the aid of external light. In its reestablishment it can move forward by about an hour a day, or move backward by ninety minutes a day, which explains why it is more perturbing to travel across time zones going east (say, from New York to Paris) than going west (from Paris to New York).
In 1998, researchers proposed that the use of blue light behind the knees reduces jet lag, possibly by irradiating the blood vessels accessible at that spot. Unfortunately, subsequent studies failed to reproduce these results (though they were initially published in the prestigious journal Science), eliminating this hope.
The best strategy seems to be exposure to light (either daylight or to a lamp used for bright light therapy) at judiciously chosen times, ideally starting several days before a flight. There are a few apps that can facilitate this; for example, Entrain, which is derived from the work of biologist Daniel Forger.
Recent research at the Stanford University School of Medicine found that the circadian rhythm can be entrained efficiently by short pulses of light (typically two-millisecond flashes ten seconds apart), especially at night. Since these can be applied through closed eyelids without waking up the subject, they provide a way to trick the body’s biological clock into adapting to an awake cycle even when asleep.
Goggles based on this principle, for example, the LumosTech Smart Sleep Mask, worn during nights just before and after a time-shifting flight, for example, could accelerate the jet-lag adjustment with minimal sleep disruption by generating light flashes during appropriately timed periods. Alternatively, innovative devices delivering extraocular light through the ear canals, for example, the Valkee Humancharger extraocular light emitter, have been shown to be effective in alleviating jet-lag symptoms. And techniques of chromotherapy such as Colorpuncture propose simple protocols for jet lag based on the activation of appropriate acupuncture reflex points with colored light.
A brief internet search reveals a multitude of lamps for bright light therapy. They have several distinguishing characteristics:
✶ Lighting technology: It is the influence on the nonvisual optic pathway that is in play here, and the circadian sensitivity spectrum is centered on blue. Two technologies are capable of emitting light with a sufficient proportion of blue: fluorescent tubes and LEDs.
✶ Brightness: The majority of models are calibrated to deliver 10,000 lux of white light, the reference brightness in most studies on SAD. Recent research tends to demonstrate equivalent effects with light intensities reduced to as low as 2,500 lux (Alotaibi, Halaki, and Chow 2016).
✶ Color: Since the circadian sensitivity spectrum of the ipRGCs culminates in blue around 460 to 490 nm, some researchers prefer to use only this waveband for bright light therapy. In doing so one can work with much lower levels of light: studies have shown that 100 lux of blue light is as beneficial as 10,000 lux of white light. Blue green (cyan or turquoise) light at 505 nm is almost as effective as blue.
✶ Format: Though most BLT devices are table lamps or “light boxes,” a few others are designed as visors that can be worn like glasses. Being portable, these have the advantage of allowing the user to go about his or her daily business. Because the light rays are aimed at the tiny area of the pupil, much less intensity is required.
✶ Orientation of the light rays: ipRGCs are more densely distributed in the lower half of the retina, onto which light from the upper visual field shines. Therefore, a light coming from above will be more efficient for bright light therapy than a light that shines on the whole visual field.
The different types of bright light therapy devices each have their own proponents, and it can be difficult to choose from among them. From the point of view of conventional medicine, one can’t go wrong with the most clinically validated solution, that of a 10,000-lux white fluorescent light box. However, this only takes into account the influence of light on the nonvisual optic pathway. From the perspective of this book, other factors come into play (the risks of certain forms of lighting are discussed in chapter 6). These factors tend to discourage the use of fluorescents because of the intense lines in their light spectrum generated by the presence of toxic mercury, which is at the basis of this technology. LEDs are the preferred replacement. And even if it may be tempting to choose blue or turquoise light, the spectrum of which is optimal for this application, from a chromotherapeutic point of view each color has a profound psychophysiological influence. White light, being neutral, is less likely to be disturbing than intense pure colors, which do not necessarily correspond to our immediate needs.
Another key factor is the blue light hazard (BLH) which determines the risk of damage to the retinal photoreceptors caused by higher-energy photons, particularly those of the deep blue wavelengths ranging from 420 to 470 nm. According to this criterion, the use of turquoise at 505 nm is preferable because the risk of BLH is reduced, while the effects on the ipRGCs are largely maintained. But even then the danger is substantial for long-term use. The overlap of the action spectra of the ipRGCs’ circadian sensitivity and that of the BLH is such that one cannot be activated without the other’s engagement.
Note: For all applications other than the mild “winter blues” it is not recommended to experiment with bright light therapy without being under the supervision of a trained specialist. Despite there being few associated side effects with bright light therapy, because it is a powerful therapeutic modality, prudence in its use is advised.
The danger of BLH (discussed in chapter 6) can be reduced by adding an infrared component to the light source. The infrared compensates for retinal degradation through the action of photobiomodulation. Unfortunately, as far as I know, no lamp on the market today has this property.
In the end there is still no device for bright light therapy that takes into account all of these factors. The ideal lamp would probably have a white spectrum of moderate intensity, including an appropriate proportion of infrared, and be oriented to shine from above.
One can only hope that such a lamp will eventually come on the market. Meanwhile, my favorite solution for occasional use, such as in the case of jet lag, is a white light LED visor, for example, the Luminette visor. For long-term use one could consider using a white LED light box and putting a source of incandescent (or halogen) light next to it as a way of adding infrared to mitigate blue light hazard (BLH).
©2018 by Anadi Martel.
Reprinted with permission of the publisher,
Healing Arts Press. www.InnerTraditions.com
Light Therapies: A Complete Guide to the Healing Power of Light
by Anadi Martel
(Originally published in French: Le pouvoir de la lumière: À l'aube d'une nouvelle médecine)
A comprehensive guide to the therapeutic benefits of light and color and how they affect our physical and psychological well-being. * Shares scientific research on how different wavelengths of light influence our cells, brain function, sleep patterns, and emotional stability * Examines several forms of light therapy, including chromotherapy, heliotherapy, actinotherapy, and thermotherapy * Explains how to use light and color therapy, maximize the benefits of sunlight, and avoid the health risks of new light sources such as compact fluorescents and LEDs.
About the Author
Anadi Martel is a physicist and electronics designer, who has acted as a consultant for IMAX, Cirque du Soleil, and the Metropolitan Opera of New York. For more than 30 years he has researched the therapeutic properties of light and the interaction between technology and consciousness, leading to the creation of the Sensora multisensorial system. His sound spatialization devices have been used around the world, including by NASA. He serves as President of the International Light Association (ILA) and lives in Quebec.